The invention relates to methods and apparatuses for generating an indication of speed on the basis of a position transmitter. The invention also relates to closing apparatuses with a means for detecting trapping for the purpose of implementing a trapping protection function.
Electrical drive units are used in a multiplicity of applications and are used, in particular, to cause a movement of elements. For example, drive units may be used in automatic closing apparatuses, for example electrical window regulators or sliding roofs in motor vehicles. In order to increase the comfort for the passengers there, an additional function may be implemented, with the result that the operator must only start the opening or closing movement of the window by actuating an actuating element once for a particular direction, that is to say an opening or closing direction. The window is then automatically moved even after releasing the actuation of the actuating element.
In the case of such a function or a comparable function, the operator does not need to continue to monitor the further movement of the element or the window and there is therefore the risk of objects or body parts being trapped between the movable part and a stationary part.
In particular, electrical window regulators must be provided with a so-called anti-trapping function which detects a trapped object or body part and releases it from the trapped state again.
Trapping may be detected by different types of sensors on the basis of measurement variables. For example, a pressure sensor, such as a piezoelectric sensor, on a stop edge, toward which the movable element moves, can detect when the element strikes the stop edge. The movement of the movable element or the rotational movement of the drive unit driving the movable element can be detected using a motion sensor, for example a Hall sensor, an AMR sensor, a GMR sensor or the like. Alternatively or additionally, a current sensor may also be provided for the purpose of detecting a motor current of the drive unit.
For reasons of cost, speed sensors based on magnetic or optical position transmitters, which are directly arranged on an output shaft of the drive unit and output a pulse or a level change in the event of a movement by a particular angular range, are used to implement such functions. The interval of time between the edges generated by the position transmitter depends directly in this case on the rotational speed of the drive unit. In this case, the rotational speed is determined from the interval of time between the edges or from their frequency. For this reason, the temporal resolution of the rotational speed indication determined using the position transmitters naturally fluctuates since the interval of time between the individual edges of the position transmitter becomes longer, in particular at low rotational speeds. This results in there being no current rotational speed indication within the period between two edges. In time-critical applications in particular, such as the trapping protection function in electrical closing apparatuses, the period during which no current rotational speed indication is provided may be too long to meet the legal requirements imposed on the reaction speed and sensitivity of the detection of trapping of an object or body part.
Therefore, the object of the present invention is to provide a method and an apparatus which can also be used to provide a continuous rotational speed indication when using a position transmitter as the rotational speed or motion sensor.